<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div{
            /* 半圆 */
            /* width: 800px;
            height: 400px;
            background: brown;
            margin: 0 auto;
            border-radius: 0px 0px 400px 400px; */
            /* 扇形 */
            /* width: 400px;
            height: 400px;
            background: brown;
            margin: 0 auto;
            border-radius: 400px 0 0 0 ; */
            /* 椭圆的扇形 */
            width: 800px;
            height: 400px;
            background: brown;
            margin: 0 auto;
            border-radius: 800px 0 0 0/400px 0 0 0  ;
        }
    </style>
</head>
<body>
    <div></div>
</body>
</html>